Stabilizers for polymers and polymers stabilized thereby

ABSTRACT

New derivatives of N,N&#39;-4-piperidyl-tetralkyl-substituted alkylene diamines are disclosed. These new compounds are useful for stabilizing thermoplastic polymers, in particular polyolefins, against sunlight, heat and oxidation. A process for producing the new compounds is also disclosed, as well as the use thereof as stabilizers of polymers and polymeric compositions.

THE PRIOR ART

As is known, the synthetic polymers in general suffer a certaindegradation of their chemical-physical properties when they are exposedto sunlight or to other sources of ultraviolet light and when subjectedto the various heat treatments during processing thereof.

It is also known, and usual, to add stabilizing substances to thesynthetic polymers in order to improve their stability to sunlight andheat. For this purpose use is generally made of small quantities ofbenzophenones, benzotriazoles, amino-phenols, triazole compounds,phosphites, thiophosphites, kelates of transition metals, organo-stanniccompounds, carbamates and thiocarbamates, esters of α-cyanoacrylic acid,etc., these substances being used either alone or in suitablecombinations with each other.

The compounds mentioned, especially when employed in suitablecombinations with each other, stabilize the synthetic polymers to apractically acceptable extent, but do not completely solve the problem.

It is known, too, that certain derivatives of2,2,6,6-tetra-alkyl-piperidine are excellent stabilizers to sunlight andheat. In particular, U.S. Pat. No. 3,904,581 describes polymericcompositions stabilized with derivatives of4-amino-2,2,6,6-tetra-alkyl-piperidine having the general formula:##STR1## in which R₁ and R₂ may be methyl, R₃ may be an alkyl having 1to 8 carbon atoms and, when n is 2, group R₄ may be, among other things,an alkylene having 2 to 6 carbon atoms and R₅ may be hydrogen.

Said piperidine derivatives considerably improve the photo- andthermo-stability of the synthetic polymers, but in order to reachsatisfactory values it is necessary to use them in combination withother stabilizers. Furthermore, when they are used for thin articles,such as films and fibers, they are easily extracted during the washingsor in general when brought into contact with water or with aqueoussolutions of surfactants.

THE PRESENT INVENTION

An object of this invention is to provide a new class of stabilizers forthermoplastic synthetic polymers which are more effective than the priorart stabilizers in protecting said polymers against sunlight and heat,and more resistant to being removed when the polymers or polymericcompositions comprising them are brought into contact with aqueousmedia, as during washing.

This and other objects are achieved by this invention in accordance withwhich the thermoplastic synthetic polymers are stabilized by newderivatives of N,N'-piperidyl-tetraalkyl-substituted alkylene diaminesof the general formula: ##STR2## wherein: each of R₁, R₂, R₃ and R₄,which may be the same or different, may be an alkyl having 1 to 4 carbonatoms; R₅ is hydrogen or an alkyl having 1 to 4 carbon atoms; A is analkylene group having 2 to 10 carbon atoms or a cycloalkylene groupcontaining 4 to 10 carbon atoms; x and y are integers from 0 to 10; R₆,R₇, R₈ and R₉, which may be the same or different, are each a linear orramified alkyl group having 1 to 8 carbon atoms or an aralkyl grouphaving 7 to 18 carbon atoms, and B is hydrogen, a linear or ramifiedalkyl group having 1 to 8 carbon atoms, a cycloalkyl group, an aryl oran alkyl-aryl group having 4 to 18 carbon atoms, a phosphite group##STR3## or a phosphate group ##STR4## in which R₁₀ and R₁₁, the same ordifferent, may each be an alkyl radical containing 1 to 6 carbon atoms,an alkylene radical having 2 to 6 carbon atoms, a cycloalkyl, aryl,arylene, alkyl-aryl group having 4 to 18 carbon atoms, or R₁₀ and R₁₁together may form a simple or substituted aromatic nucleus.

The presently preferred derivatives of theN,N'-4-piperidyl-tetralkyl-substituted alkylene diamines having generalformula (I) for use in the practice of this invention are those in whichR₁, R₂, R₃ and R₄ are methyl; R₅ is hydrogen; x and y are integers from2 to 6; each of R₆, R₇, R₈ and R₉ are tert.butyl and B is hydrogen or##STR5##

The term "synthetic thermoplastic polymers", as used in thisspecification and in the appended claims, includes:

polyolefins including the homopolymers of olefins such as low and highdensity polyethylene, polypropylene, polystyrene, polybutadiene,polyisopropene and the like, and copolymers of the olefins with otherethylenically unsaturated monomers such as ethylene-propylenecopolymers, ethylene-butene copolymers, ethylene-vinylacetatecopolymers, styrene-butadiene copolymers, styrene-acrylonitrilecopolymers and acrylonitrile-styrene-butadiene copolymers;

polyvinyl chloride and polyvinylidene chloride, including both thehomopolymers and the copolymers of vinyl chloride and of vinylidenechloride with each other or each with vinyl acetate or otherethylenically unsaturated monomers;

polyacetals such as polyoxymethylene and polyoxyethylene;

polyesters such as polyethylene terephthalate;

polyamides such as nylon 6, nylon 6-6 and nylon 6-10, and

polyurethanes

Such synthetic polymers can be employed either as powder or as granules,or as shaped articles, e.g. fibers, films, sheets and other shapedarticles and also as latex and foams.

The presently preferred synthetic polymers for use in practice of thisinvention are the polyolefins deriving from monomers having the generalformula:

    R--CH═CH.sub.2

wherein R is an alkyl or aryl group, or a hydrogen atom.

The presently preferred polyolefin is propylene, consisting prevailinglyof isotactic macromolecules and obtained by the polymerization ofpropylene in the presence of stereospecific catalysts.

The amount of the derivative ofN,N'-4-piperidyl-2,2,6,6-tetralkyl-substituted alkylene diamine to beadded to the synthetic polymer according to the present invention is inan amount sufficient to prevent degradation of the polymer. This amountcan vary in a wide range as a function of type, properties andparticular uses of the synthetic polymer to be stabilized. Generally,said derivatives can be added to the polymer in amounts comprisedbetween 0.01 and 5.0% by weight, based on the polymer weight; inpractice, however, the effective amount varies as a function of the typeof polymer to be stabilized. Thus, for instance, in the case ofpolyolefins, an effective amount can range from 0.01 to 2% by weight; inthe case of polyvinyl chloride and of polyvinylidene chloride suchamount can vary from 0.01 to 1% by weight, while in the case ofpolyurethanes and of polyamides the effective amount varies from 0.01 to5% by weight.

The above-mentioned stabilizers can be employed either alone or inadmixture with other known additives such as antioxidants, adsorbents ofultraviolet rays, pigments, fillers, basic nitrogen containingpolycondensates, stabilizers, etc. Some examples of such additives areoxy-benzotriazoles, oxy-benzophenones, Ni-stabilizers, metal soaps,phenolic antioxidants, phosphites, thioesters, hydroquinone derivatives,triazine compounds, acryl-amino-phenols, benzyl-phosphonates, etc. Suchadditives may be employed along with the derivatives of alkylene-diaminehaving general formula (I) according to the present invention, at aratio by weight ranging from 0.5:1 to 3:1.

The incorporation of the alkylene diamine (I) or of the mixturecontaining said derivative with the synthetic polymer can be carried outaccording to different conventional procedures and at any stage prior toor during the manufacturing of the shaped article from said polymer.Thus, for example, the additives in powder form can be simply mixed withthe polymer under stirring; or the polymer can be mixed with a solutionof the stabilizers in a suitable solvent, whereupon said solvent isevaporated; or the stabilizers can be added to the polymer at theconclusion of polymerization.

Furthermore the stabilizing effect can be achieved by applying thestabilizer to the manufactured article, for example by immersing thearticle in a solution or dispersion of the stabilizers and bysuccessively evaporating the solvent or the dispersant.

The alkylene-diamine derivatives having the above-indicated generalformula (I) are characterized in that they possess:

a high degree of stabilizing activity, as compared with the knownstabilizers, with respect to the synthetic thermoplastic polymers,towards the degradation caused by heat, sunlight and ageing;

good consistency with the synthetic thermoplastic polymers without anyappreciable degree of coloring;

good consistency with the other known stabilizers or additives withoutcoloring the polymer to be stabilized or reducing their stabilizingactivity;

low degree of thermal sublimation or exudation, and

low degree of extraction during the treatment with water or with aqueoussolutions.

The derivatives of N,N'-4-piperidyl-2,2,6,6-tetralkyl-substitutedalkylene diamine are preferably synthesized according to the followingscheme: ##STR6##

The reaction (II)→(III) can be carried out by reacting compound (II)with an alkylene diamine and hydrogen under pressure in the presence ofa hydrogenation catalyst such as platinum.

The reaction (III)→(IV) can be conducted in an alcoholic solution byreacting the diamine (III) with a ω-halogenated alcohol in the presenceof an agent capable of fixing the acid.

The reaction (IV)→(V) can be conducted by reacting a dialcohol (IV) witha derivative of an aliphatic acid, either containing, or not containing,phosphorus in the presence of acid or basic catalysts.

The following non-limiting examples are given for a more detailedunderstanding of the present invention and for enabling the art topractice the same. Unless otherwise specified, all the parts in theexamples are to be understood as parts by weight.

EXAMPLE 1 Preparation of3-[3,5-di-tert.butyl-4-hydroxyphenyl]di-propionate of bis[N,N'-diethyl-N,N'-(2,2,6,6-tetramethyl-4-piperidyl)]1,6-hexamethylenediamine

In a 500 cc flask equipped with a stirrer, a thermometer and a refluxcooler, 45 g (0.55 mole) of ethylene chlorohydrin dissolved in 50 cc ofmethanol were added to a solution of 100 g (0.25 mole) ofN,N'-bis-(2,2,6,6-tetramethyl-4-piperidyl) 1,6-hexamethylene diaminedissolved in 120 cc of methanol.

The mixture was heated at reflux to boiling and 22 g (0.55 mole) of NaOHin tablets were gradually added thereto in 8 hours. Following theaddition of NaOH, the mass was heated at reflux for a further 2 hours,then cooled down and filtered to separate the sodium chloride that hadformed. The filtrate was dried to evaporate the methanol, whereupon theresidue was crystallized in dioxane. The resulting product had a meltingpoint of 139°-141° C. and a content of N=11.6% (calculated value:11.7%).

24.1 g (0.05 mole) of the compound so obtained were mixed in a 250 ccflask with 29.2 g (0.1 mole) of3(3,5-di-tert.butyl-4-hydroxyphenyl)propionate of methyl and 0.3 g oflithium hydroxide. The mixture was heated to 140° C. for 1 hour understirring and then to 130° C. for 2.5 hours under vacuum at 18 mm Hg ofresidual pressure. The resulting product was dissolved in hexane andwashed with water containing a few drops of acetic acid in a separatoryfunnel.

After separation and removal of the hexane, a compound was obtained,which was a very viscous oil. The elemental analysis gave the followingresults:

    ______________________________________                                               Found values Calculated values                                         ______________________________________                                        C =      73.5%          74.4%                                                 H =      10.7%          10.4%                                                 N =      5.4%           5.6%                                                  ______________________________________                                    

corresponding to the compound: ##STR7##

Stabilization Tests

100 cc of chloroform containing, dissolved therein,3[3,5-di-tert.butyl-4-hydroxyphenyl]di-propionate of bis[N,N'-di-ethyl-N,N'-(2,2,6,6-tetramethyl-4-piperidyl)]1,6-hexamethylenediamine, as prepared in Example 1 and in amounts as indicated in TableI, were added to 100 g of non-stabilized polypropylene (having anintrinsic viscosity, measured in tetralin at 130° C., of 162 cc/g, aresidue after extraction of the crude polymerizate with n-heptane of96.5%, and ashes=80 ppm).

Each mixture was stirred for about 6 hours at room temperature in arotary evaporator and then dried at 0.01 mm Hg at 50° C. for 1 hours.The additioned powder so obtained was extruded in a Brabender extruderat 220° C. and granulated. The granules were molded to films at 200° C.for 3 minutes between two square steel plates measuring 20×20 cm, andunder a load of 1000 kg.

The films so obtained exhibited a uniform thickness of 50-60μ and werepractically colorless and homogeneous. On the films so prepared, thethermo-oxidative stability, at different temperatures and at 760 mm Hgof oxygen, and the photo-oxidative stability were determined. Thethermo-oxidation induction period (Ip), intended as the time required toget a quick increase of the oxygen absorption rate was taken asthermo-oxidative stability value. The photo-oxidative stability test wascarried out by exposing the films in an apparatus of the type Xenotest450 manufactured by Messrs. Hanau and by determining on said films theconcentration variations of the carbonyl groups by means of I.R.spectrometry and the variation of the mechanical properties by means ofbending tests.

The induction period (Ip) necessary to bring about a rapid increase inthe formation rate of the carbonyl groups was taken as photo-oxidativestability value, and the exposure time to the Xenotest, necessary tocause the rupture of the film by means of one bending only, asembrittling time.

To determine the thermo-oxidative stability, 0.2 g of each of the filmsobtained was cut to pieces and introduced into a cell of about 50 cm³,wherein an oxygen atmosphere was created by repeatedly removing andintroducing oxygen. The cell was connected with an oxygen measuringdevice equipped with a recorder of the volumes absorbed. The cell wasimmersed in a thermostatic bath maintained at a temperature of 170° C.The induction period (Ip) values measured on the films are recorded inTable I.

To determine the photo-oxidative degradation, some cut pieces of filmwere mounted on the proper supports of apparatus Xenotest 450 andexposed to the light of a xenon lamp 4500 W, filtered to have anemission spectrum as similar as possible to the solar spectrum. Thetemperature in the exposure chamber was kept at 50°±2° C. and therelative humidity at 35±5%. At intervals of time, film samples weretaken in order to measure the I.R. absorption in proximity of the wavelength of 1720 cm⁻¹, corresponding to the absorption of the carbonylgroups. With a view to evaluating the concentration of the carbonylgroups, a conventional value of the molar absorption coefficient equalto 300 l/mole×cm was assumed. The induction period (Ip) values measuredon the films are recorded in Table I.

                  TABLE I                                                         ______________________________________                                                            Photo-oxidative                                                  Thermo-oxidative                                                                           stability                                                 Stabilizer                                                                             stability               Embrittlement                                % by weight                                                                            Ip in h. Temp. ° C.                                                                       Ip in H.                                                                             time in hours                              ______________________________________                                        --       0        170        60     70                                        0.25     6.4      170        850    920                                       0.50     14       170       1400   1500                                       0.75     27       170       1600   1750                                       ______________________________________                                    

The thermo-oxidative stability tests recorded above were conducted alsoon the mixture consisting ofpolypropylene/3[3,5-di-tert.butyl-4-hydroxyphenyl]di-propionate ofbis[N,N'-diethyl-N,N'(2,2,6,6-tetramethyl-4-piperidyl]1,6-hexamethylenediamine in the same ratios indicated hereinbefore. The results obtainedwere wholly like those obtained from the film, which proved that the hotprocessing necessary to obtain the films did not sensibly alter thecomposition stability.

EXAMPLE 2 Preparation of3-[3,5-di-tert.butyl-4(o-phenylene-phosphorosyl) phenyl]di-propionate ofbis[N,N'-di-ethyl-N,N'(2,2,6,6-tetramethyl-4-piperidyl)]1,6-hexamethylenediamine

In a 250 cc flask, 30 g (0.03 mole) of3[3,5-di-tert.butyl-4-hydroxy-phenyl]di-propionate ofbis[N,N'-di-ethyl-N,N'(2,2,6,6-tetramethyl-4-piperidyl)]1,6-hexamethylenediamine, prepared according to Example 1, were dissolved in 100 cc ofbenzene. The solution was cooled to +5° C. and a solution of 10.5 g(0.06 mole) of o.phenylene chlorophosphite in 20 cc of benzol wasgradually added thereto in 1 hour under continuous stirring. The mixturewas left 2 hours at room temperature, after which it was cooled to 0° C.while gaseous ammonia was blown in for 4 hours. The ammonium chloride soformed was separated by filtration and evaporated under vacuum. Theresulting product was solid, white-cream colored, had a melting point of78°-80° C. and the following elemental analysis:

    ______________________________________                                        C = 68.7%        N = 4.1%                                                     H =  8.8%        P = 4.7%                                                     ______________________________________                                    

in accordance with the centesimal calculated composition

    ______________________________________                                        C = 69.50%       N = 4.38%                                                    H =  8.76%       P = 4.85%                                                    ______________________________________                                    

corresponding to the compound: ##STR8##

Stabilization Tests

By operating according to Example 1, films having a uniform thickness of50-60μ were prepared. The samples were subjected to the thermo-oxidativeand photo-oxidative stability tests of Example 1, the results obtainedbeing recorded in Table II.

                  TABLE II                                                        ______________________________________                                                            Photo-oxidative                                                  Thermo-oxidative                                                                           stability                                                 Stabilizer                                                                             stability               Embrittlement                                % by weight                                                                            Ip in h. Temp. ° C.                                                                       Ip in h.                                                                             time in hours                              ______________________________________                                        --       0        170        60     70                                        0.3      9.6      170        750    780                                       0.5      17.8     170       1500   1600                                       ______________________________________                                    

What we claim is:
 1. Derivatives of N,N'-piperidyl-tetralkyl-substitutedalkylene diamine having the formula (I): ##STR9## in which: each of R₁,R₂, R₃ and R₄, which may be the same or different, is an alkyl having 1to 4 carbon atoms; R₅ is hydrogen or an alkyl having 1 to 4 carbonatoms; A is an alkylene group having 2 to 10 carbon atoms or acycloalkylene group having 4 to 10 carbon atoms; x and y are integersfrom 0 to 10; each of R₆, R₇, R₈ and R₉, which may be the same ordifferent, is a linear or ramified alkyl group having 1 to 8 carbonatoms or an aralkyl group having 7 to 18 carbon atoms, and B ishydrogen, a linear or ramified alkyl group having 1 to 8 carbon atoms, acycloalkyl, aryl or alkyl-aryl group having 4 to 18 carbon atoms, aphosphite group ##STR10## or a phosphate group ##STR11## in which eachof R₁₀ and R₁₁, which may be the same or different, is an alkyl radicalhaving 1 to 6 carbon atoms, an alkenyl radical having 2 to 6 carbonatoms, a cycloalkyl, aryl, arylene or alkyl-aryl radical having 4 to 18carbon atoms or R₁₀ and R₁₁ together form an aromatic nucleus, or asubstituted aromatic nucleus.
 2. Derivatives of theN,N'-piperidyl-tetralkyl-substituted alkylene diamine according to claim1, in which, in formula (I), R₁, R₂, R₃ and R₄ are methyl; R₅ ishydrogen; x and y is each an integer from 2 to 6; each of R₆, R₇, R₈ andR₉ is tert.butyl and B is hydrogen or the group ##STR12## 3.Compositions comprising synthetic thermoplastic polymers stabilized tosunlight, to heat and to ageing, and having incorporated therein, in anamount sufficient to prevent degradation of the polymer, a compoundhaving formula: ##STR13## in which: each of R₁, R₂, R₃ and R₄, which maybe the same or different, represent an alkyl having 1 to 4 carbon atoms;R₅ is hydrogen or an alkyl having 1 to 4 carbon atoms; A is an alkylenegroup having 2 to 10 carbon atoms or a cycloalkylene group having 4 to10 carbon atoms; x and y are integers from 0 to 10; each of R₆, R₇, R₈and R₉, which may be the same or different, is a linear or ramifiedalkyl group having 1 to 8 carbon atoms, or an aralkyl group having 7 to18 carbon atoms, and B is hydrogen, a linear or ramified alkyl grouphaving 1 to 8 carbon atoms, a cycloalkyl, aryl or alkylaryl group having4 to 18 carbon atoms, a phosphite group ##STR14## or a phosphate group##STR15## in which R₁₀ and R₁₁, which may be the same or different,represent an alkyl radical having 1 to 6 carbon atoms, an alkenylradical having 2 to 6 carbon atoms, a cycloalkyl, aryl, arylene oralkyl-aryl radical having 4 to 18 carbon atoms, or R₁₀ and R₁₁ togetherform an aromatic necleus, or a substituted aromatic nucleus. 4.Compositions according to claim 3, in which, in formula (I), R₁, R₂, R₃and R₄ are methyl; R₅ is hydrogen; x and y are each an integer from 2 to6; each of R₆, R₇, R₈ and R₉ is tert.butyl and B is hydrogen or thegroup ##STR16##
 5. Compositions according to claim 3, in which thecompound of general formula (I) is present in an amount ranging from0.01 to 5% by weight on the weight of the polymer.
 6. Compositionsaccording to claim 3, in which the polymer is polyolefin. 7.Compositions according to claim 6, in which the compound of generalformula (I) is present in an amount ranging from 0.01 to 2% by weight onthe weight of the polyolefin.
 8. Compositions according to claim 3, inwhich the polymer is polyvinyl chloride or polyvinylidene chloride. 9.Compositions according to claim 8, in which the compound of generalformula (I) is contained in an amount ranging from 0.01 to 1% by weighton the weight of the polymer.
 10. Compositions according to claim 3, inwhich the polymer is a polyurethane or a polyamide.
 11. Compositionsaccording to claim 10, in which the compound of general formula (I) iscontained in an amount ranging from 0.01 to 5% by weight on the weightof the polymer.
 12. Compositions according to claim 3, in which compound(I) is employed in admixture with at least one adjuvant. 13.Compositions according to claim 12 in which the adjuvants are selectedfrom the group consisting of antioxidants, ultraviolet ray absorbents,pigments, fillers, basic nitrogen containing polycondensates, andauxiliary stabilizers.
 14. Compositions according to claim 12, in whichthe ratio of adjuvant or adjuvants to the compound of formula (I) isfrom 0.5:1 to 3:1.